Large aperture extended range zoom lens

ABSTRACT

Disclosed is an optical design for a variable focal length lens of large effective aperture which is focusable over an extended range including the &#34;macro&#34; range and is provided with a high degree of correction.

This invention relates to a variable focal length lens of large effective aperture, and more particularly to a variable focal length lens, focusable over an extended range, and highly corrected over a large range of magnification.

Many zoom lenses or variable equivalent focal length lenses have been designed having moderate effective apertures insofar as are desired to be competitive with the existing market of photographic equipment, such as motion picture cameras. Recently, another generation of zoom lenses has been designed having unusually large apertures in the f/1.2 class. Generally, these lenses have had magnification ratios not exceeding three-to-one. Thus, the benefit of the high effective aperture has been offset against a low magnification ratio. Other lenses of lesser apertures, although of similar or slightly greater magnification ratios to the high aperture lenses, have been designed for focusing in a range of less than the normal range of approximately 1 meter to infinity. This less than normal focusing range enabling focusing from several millimeters from the lens to the closest distance of the normal range is referred to as the "Macro" range. Most lenses with a high aperture or a high magnification ratio are not capable of maintaining the required high degree of correction when focusing in the macro range. Hence, only a few relatively special, and therefore generally expensive lenses have been designed and are available having the combination of features incorporated in the present lens design. Also, because of the expense of these lenses, most have not been competitive so as to receive acceptance in the mass market by the "home" movie makers.

Another object of the invention is to provide a relatively compact and relatively inexpensive zoom lens highly corrected over a magnification range greater than the more conventional three-to-one range of zoom lenses of comparable large effective apertures.

It is to be understood that the terms "front" and "rear" as used herein refer to the ends of the objective respectively nearer the long and short conjugates thereof.

Other objects and advantages of the invention will become apparent from the detailed description which follows when taken in conjunction with the accompanying drawings in which:

FIG. 1 is a diagrammatic sectional view of a preferred optical system according to the present invention;

FIGS. 2A to 2H are graphical representations of the various aberrations of the lens system shown in FIG. 1 and having the design data given in Table 1 when in the wide angle mode; and

FIGS. 3A to 3H are similar graphical representations of the Table 1 lens system when in the telephoto mode.

Referring to the drawings, a zoom lens or variable equivalent focal length objective lens is shown. Particularly, the lens is highly corrected over a relatively large magnification range, and is capable of focus in the macro range as well as the normal range. Further, the lens has a relatively large effective aperture when compared to other lens designs having the zoom range.

The lens includes a positive first component C₁, starting at the ray entrance side of the optical system, which component is adjustable axially through a short distance for focusing of the optical system throughout a range of approximately 1 meter to infinity. Component C₂ is a variator or negative component variable along the axis of the optical system for varying the equivalent focal length of the objective. The equivalent focal length is variable over greater than a six-to-one range of magnification while maintaining a high degree of optical correction for a large aperture of at least f/1.2 throughout the range. Component C₃ is a component adjustable axially upon axial adjustment of the variator, to function as a compensator for correcting berrations caused by varying the focal length of the optical system. C₂ is independently adjustable for focusing of the optical system in the macro range. Component C₄ is a fixed lens member for further collimating rays exiting the compensator component C₃. Rear component C₅ is a prime lens group forming an afocal system with the earlier described components.

The front component C₁, comprises a front biconvex cemented doublet L₁, L₂, and a rear singlet L₃, predominately convex forwardly and spaced close to the doublet L₁, L₂. Air spaced from the rear of the singlet L₃ and adjustable relative thereto is component C₂ which comprises a front negative meniscus singlet L₄ convex forwardly and a rear biconcave, cemented doublet L₅, L₆ predominately concave forwardly. The doublet has collective internal contact surfaces R₁₀, R₁₁.

Component C₃ is variably air spaced relative to component C₂ and the following component C₄. Component C₃ comprises a positive doublet L₇, L₈ predominately convex rearwardly. During a zooming or focal length varying operation, the component C₃ is moved axially at a rate proportional to the rate of movement of component C₂. However, for macro focusing action, the driver (not shown) of the components C₂ and C₃ by which axial adjustment thereof is accomplished is disconnected from component C₃ to cause that component to remain stationary while component C₂ is adjusted axially for focusing.

Component C₄ is fixed ahead of the stop of the optical system and comprises a front negative meniscus singlet L₁₀ and a rear positive meniscus singlet L₁₁ which together form a substantially afocal system cooperating with the rear prime lens system C₅.

Component C₅ comprises a front biconvex singlet L₁₂, spaced somewhat from a negative element L₁₃. A doublet of elements L₁₄ and L₁₅ is arranged between element L₁₃ and rear element L₁₆ which is a singlet predominately convex forwardly.

The elements L₁ to L₁₆ have spherical surfaces or radii of curvature R₁ to R₃₂, axial thicknesses T₁ to T₁₆ and axial separations S₁ to S₁₇. The separations at S₁₁ and S₁₂ are sufficient to provide clearance for an aperture adjusting stop.

A preferred embodiment of the macro focusing, large aperture, zoom lens of the invention is constructed according to the table following wherein dimensions are as set forth and the refractive indices for the sodium D line and the Abbe dispersion numbers are respectively designated at N_(D) and V.

    __________________________________________________________________________     SYSTEM EFL              HALF ANGLE OF FIELD                                    at W/A - 7.61mm (.2997 in.)                                                                            25.35°                                          at T/P = 56.98mm (2.2433 in.)                                                                           3.31°                                          at MID = 25.67mm (1.0105 in.)                                                                           7.58°                                          LENS                                                                               RADII (mm.)                                                                             THICKNESS (mm.)                                                                           SPACINGS (mm)                                                                             N.sub.D                                                                           V                                        __________________________________________________________________________     1   R.sub.1 = 240.7589                                                                      T.sub.1 = 1.6510      1.755                                                                             27.6                                         R.sub.2 = -51.1988                                                                                 S.sub.1 = 0                                            2   R.sub.3 = 51.1988                                                                       T.sub.2 = 12.7000     1.620                                                                             60.4                                         R.sub.4 = 153.6954                                                                                 S.sub.2 = .1016                                        3   R.sub.5 = 43.6880                                                                       T.sub.3 = 7.7978      1.651                                                                             55.9                                         R.sub.6 = -139.7000                                                                                S.sub.3 = 4.2875 at W/A                                                          29.5554 at T/P                                                                 22.3952 at MID                                       4   R.sub.7 = 71.7550                                                                       T.sub.4 =  .8128      1.639                                                                             55.4                                         R.sub.8 = -16.5100                                                                                 S.sub.4 = 6.6294                                       5   R.sub.9 = -24.0030                                                                      T.sub.5 = .8382       1.620                                                                             60.4                                         R.sub.10 = -19.1008                                                                                S.sub.5 = 0                                            6   R.sub.11 = 19.1008                                                                      T.sub.6 = 3.5052      1.785                                                                             25.8                                         R.sub.12 = -59.9948                                                                                S.sub.6 = 38.4048 at W/A                                                         2.5857 at T/P                                                                  14.2570 at MID                                       7   R.sub.13 = 58.9280                                                                      T.sub.7 = .8890       1.805                                                                             25.4                                         R.sub.14 = -21.7424                                                                                S.sub.7 = 0                                            8   R.sub.15 = 21.7424                                                                      T.sub.8 = 5.6388      1.641                                                                             60.1                                         R.sub.16 = 30.2260                                                                                 S.sub.8 = .1016                                        9   R.sub.17 = 22.7203                                                                      T.sub.9 = 3.1496      1.691                                                                             54.9                                         R.sub. 18 = -93.1672                                                                               S.sub.9 = 1.6002 at W/A                                                          12.1514 at T/P                                                                 7.6403 at MID                                        10  R.sub.19 = -45.5168                                                                     T.sub.10 = .7112      1.691                                                                             54.9                                         R.sub.20 = -12.8016                                                                                S.sub.10 = 2.2352                                      11  R.sub.21 = 14.6431                                                                      T.sub.11 = 2.0574     1.805                                                                             25.4                                         R.sub.22 = -27.0256                                                                                S.sub.11 = 11.0490                                                               STOP                                                                         S.sub.12 = 3.5560                                      12  R.sub.23 = 18.0848                                                                      T.sub.12 = 3.6576     1.744                                                                             44.8                                         R.sub.24 = 32.8168                                                                                 S.sub.13 = 1.6002                                      13  R.sub.25 = -21.9202                                                                     T.sub.13 = .7112      1.805                                                                             25.4                                         R.sub.26 = -16.8656                                                                                S.sub.14 = .7366                                       14  R.sub.27 = 61.2140                                                                      T.sub.14 = 4.3180     1.805                                                                             25.4                                         R.sub.28 = -14.5288                                                                                S.sub.15 = 0                                           15  R.sub.29 = 14.5288                                                                      T.sub.15 = 3.25l2     1.744                                                                             44.8                                         R.sub.30 = 26.9494                                                                                 S.sub.16 = .1270                                       16  R.sub.31 = 14.7320                                                                      T.sub.16 = 2.5654     1.734                                                                             51.7                                         R.sub.32 = -463.9259                                                                               S.sub.17 = 11.4529                                     __________________________________________________________________________

In the above table, the first column lists the lens elements numerically starting at the ray entrance side of the system. The second column lists the respective radii of the elements in millimeters. The third column lists the axial thickness T of the respective elements in millimeters. The fourth column lists in millimeters the axial spacings between the respective elements, and the nominal image plane. "EFL" is the effective focal length of the lens system at wide angle condition "W/A", at telephoto condition "T/P", and at mid range condition "MID". "One-half Angle of Field" is one half the angle between the continuation of the lens axis and a line from the nodal point of the lens to the most oblique point recorded on the film when considered at the above expressed condition.

FIGS. 2A to 2H graphically represent various aberrations of the form of the optical system, as shown in FIG. 1 and having the design data recited in the above table. FIG. 2A represents correction of the rays on axis. FIG. 2B represents off axis aberrations of rays passing from the zone of the film format and through the lens transversely and tangentially. FIG. 2C represents the aberrations of the rays passing from the corner of the film format through the lens tangentially and transversely. FIG. 2D represents the radial or longitudinal aberrations from the zone of the film format of rays entering the lens at 3 o'clock, while FIG. 2E represents similar aberrations from full field or corner rays. FIG. 2F represents distortion as a percentage of a "perfect" image. FIG. 2C represents the spherical aberrations by a full line and the offense-against-sine condition by the dotted line. FIG. 2H represents the curvature of field with tangential curvature being shown in full line and sagittal curvature being shown in dashed line.

FIGS. 3A to 3H graphically represent various aberrations of the optical system with the lens adjusted to the telephoto condition, as opposed to the wide angle condition as represented in FIGS. 2A to 2H. In FIGS. 2A to 2E and 3A to 3E, the solid line represents the aberrations of a light ray at 5893 A°, the dotted line represents a light ray at 6563 A°, and the dashed line a light ray at 4861 A°. 

What I claim is:
 1. An optical system for a variable focal length lens of large effective aperture, which is focusable over an extended range, having substantially the following specification:

    ______________________________________                                         SYSTEM EFL        HALF ANGLE OF FIELD                                          at W/A =                                                                                7.61mm  (.2997 in.)                                                                         25.35°                                            at T/P =                                                                               56.98mm (2.2433 in.)                                                                          3.31°                                            at MID =                                                                               25.67mm (1.0105 in.)                                                                          7.58°                                            ______________________________________                                         LENS  RADII (mm.)  THICKNESS (mm.)                                             ______________________________________                                         1     R.sub.1 = 240.7589                                                                          T.sub.1 = 1.6510                                                  R.sub.2 = -51.1988                                                       2     R.sub.3 = 51.1988                                                                           T.sub.2 = 12.7000                                                 R.sub.4 = 153.6954                                                       3     R.sub.5 = 43.6880                                                                           T.sub.3 = 7.7978                                                  R.sub.6 = -139.7000                                                      4     R.sub.7 = 71.7550                                                                           T.sub.4 = .8128                                                   R.sub.8 = -16.5100                                                       5     R.sub.9 = -24.0030                                                                          T.sub.5 = .8382                                                   R.sub.10 = -19.1008                                                      6     R.sub.11 = 19.1008                                                                          T.sub.6 = 3.5052                                                  R.sub.12 = -59.9948                                                      7     R.sub.13 = 58.9280                                                                          T.sub.7 = .8890                                                   R.sub.14 = -21.7424                                                      8     R.sub.15 = 21.7424                                                                          T.sub.8 = 5.6388                                                  R.sub.16 = 30.2260                                                       9     R.sub.17 = 22.7203                                                                          T.sub.9 = 3.1496                                                  R.sub.18 = -93.1672                                                      10    R.sub.19 = -45.5168                                                                         T.sub.10 = .7112                                                  R.sub.20 = -12.8016                                                      11    R.sub.21 = 14.6431                                                                          T.sub.11 = 2.0574                                                 R.sub.22 = -27.0256                                                      12    R.sub.23 = 18.0848                                                                          T.sub.12 = 3.6576                                                 R.sub.24 = 32.8168                                                       13    R.sub.25 = -21.9202                                                                         T.sub.13 = .7112                                                  R.sub.26 = -16.8656                                                      14    R.sub.27 = 61.2140                                                                          T.sub.14 = 4.3180                                                 R.sub.28 = -14.5288                                                      15    R.sub.29 = 14.5288                                                                          T.sub.15 = 3.2512                                                 R.sub.30 = 26.9494                                                       16    R.sub.31 = 14.7320                                                                          T.sub.16 = 2.5654                                                 R.sub.32 = -463.9259                                                     ______________________________________                                         LENS    RADII (mm.)  SPACINGS (mm) N.sub.D                                                                             V                                      ______________________________________                                         1       R.sub.1 = 240.7589                                                                                        1.755                                                                               27.6                                           R.sub.2 = -51.1988                                                                          S.sub.1 = 0                                               2       R.sub.3 = 51.1988                                                                                         1.620                                                                               60.4 - R.sub.4 = 153.6954                                   S.sub.2 = .1016                                           3       R.sub.5 = 43.6880                                                                                         1.651                                                                               55.9                                           R.sub.6 = -139.7000                                                                         S.sub.3 = 4.2875 at W/A                                                          29.5554 at T/P                                                                 22.3952 at MID                                          4       R.sub.7 = 71.7550                                                                                         1.639                                                                               55.4                                           R.sub.8 = -16.5100                                                                          S.sub.4 = 6.6294                                          5       R.sub.9 = -24.0030                                                                                        1.620                                                                               60.4                                           R.sub.10 = -19.1008                                                                         S.sub.5 = 0                                               6       R.sub.11 = 19.1008                                                                                        1.785                                                                               25.8                                           R.sub.12 = -59.9948                                                                         S.sub.6 = 38.4048 at W/A                                                         2.5857 at T/P                                                                  14.2570 at MID                                          7       R.sub.13 = 58.9280                                                                                        1.805                                                                               25.4                                           R.sub.14 = -21.7424                                                                         S.sub.7 = 0                                               8       R.sub.15 = 21.7424                                                                                        1.641                                                                               60.1                                           R.sub.16 = 30.2260                                                                          S.sub.8 = .1016                                           9       R.sub.17 = 22.7203                                                                                        1.691                                                                               54.9                                           R.sub.18 = -93.1672                                                                         S.sub.9 =1.6002 at W/A                                                           12.1514 at T/P                                                                 7.6403 at MID                                           10      R.sub.19 = -45.5168                                                                                       1.691                                                                               54.9                                           R.sub.20 = -12.8016                                                                         S.sub.10 = 2.2352                                         11      R.sub.21 = 14.6431                                                                                        1.805                                                                               25.4                                           R.sub.22 = -27.0256                                                                         S.sub.11 = 11.0490                                                             ----STOP----                                                                   S.sub.12 = 3.5560                                         12      R.sub.23 = 18.0848                                                                                        1.744                                                                               44.8                                           R.sub.24 = 32.8168                                                                          S.sub.13 = 1.6002                                         13      R.sub.25 = -21.9202                                                                                       1.805                                                                               25.4                                           R.sub.26 = -16.8656                                                                         S.sub.14 = .7336                                          14      R.sub.27 = 61.2140                                                                                        1.805                                                                               25.4                                           R.sub.28 = -14.5288                                                                         S.sub.15 = 0                                              15      R.sub.29 = 14.5288                                                                                        1.744                                                                               44.8                                           R.sub.30 = 26.9494                                                                          S.sub.16 = .1270                                          16      R.sub.31 = 14.7320                                                                                        1.734                                                                               51.7                                           R.sub.32 = -463.9259                                                                        S.sub.17 = 11.4529                                        ______________________________________                                    

wherein the first column lists the lens elements numerically starting at the ray entrance side of the system; the second column lists the respective base radii R₁ to R₃₂ ; the third column lists the thicknesses T₁ -T₁₆ of the respective elements; the fourth column lists the axial spacings S₁ to S₁₇ between the respective elements, and stop, and the image plane; and the fifth and sixth columns respectively list the index of refraction for the Sodium D line N_(D) and the dispersive index V of the optical materials of the respective elements. 